Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
1 · Low
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 13 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanche danger remains MODERATE near treeline and below treeline on NW-N-NE aspects on slopes steeper than 32 degrees due to lingering persistent slab instability.

Signs of snowpack instability are still observed on a near daily basis. Human triggered avalanches are possible. 

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Persistent slab instability remains ongoing near treeline and below treeline on NW-N-NE aspects. The faceted Dec 7 persistent weak layer is slowly gaining strength, but not enough to make much difference in terms of reducing overall avalanche danger.

    Knowing that the ongoing going avalanche problem is a persistent slab issue, finding a lack of evidence of instability while moving around the backcountry should be cause for concern. Anyone finding themselves in that position and desiring to commit to NW-N-NE aspects on slopes steeper than 32 degrees is advised to spend additional time assessing snowpack stability on a slope by slope basis in order to find the missing pieces of data.

Avalanche Discussion

It has been three weeks since the last significant snowfall and obvious clues of instability are still apparent. Yesterday on Silver Peak (Pole Creek area), travel on slopes that had not experienced traffic since the Dec 7 snowfall event caused localized cracking and skier triggered collapsing to occur. One of the collapses radiated out approximately 60 feet from the trigger point. This matched well with much of the other recent snowpit data from around the forecast area that has repeatedly shown that the faceted Dec 7 persistent weak layer retains the ability to propagate fractures once collapsed.

Spacial variability is increasing around the forecast area in regards to stability improvements of the Dec 7 faceted weak layer. The amount of force required to trigger weak layer collapse and the ability for that collapse to propagate are becoming more variable from one location to another. In some spots, strength increases in the Dec 7 persistent weak layer are highly evident while in other areas the strength gains have been much more modest. Either way, the data still indicates that human triggered avalanches are possible in many locations around the forecast area.

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